If you have access to a CRO (Oscilloscope) then it is simple. Take a tapethat you trust (possibly one you recorded when the D7 was new) and play it.Hook input 1 of the CRO to TPRF and input 2 to TPSWP. Sync the CRO to input2 and then just adjust the guides till you get the best looking envelope.

Simple. If you have no access to a CRO, you can put the deck in FF mode andadjuse the right guide till you get good A-Time increments. If the guide istoo low, you lose A-Time in FF mode. Just raise it till you get A-Timeproperly, and drop down to normal play and adjust the left guide till itsounds right. Of course, it pays to take a piece of paper and draw down theoriginal positions.

You are also assuming it is an alignment problem. It could be head wear. Totest this, take the D7 apart and perform this simple test:

i) Take pin 100 of IC 506 and ground it.

Then disconnet the ground and

ii) Take pin 100 of IC 506 and connect to pin 55/54 of IC 506.

While playing a tape, you should hear identical sound in both i) and ii).If the D7 goes dead silent on either i) or ii), or the distortion ismarkedly worse in i) or ii), then it is head damage (or wear). If thedistortion is equally bad then it is an alignment problem. Of course, itwould help a lot if you had a CRO, in which case you just compare A/Benvelope shape.

>Before we all go off thinking that humans can hear sounds at 54kHz, we>should perhaps consider other possibilities.>>1. If any part of this interference was digitized or if any part of>the audio signal was digitized, you would DEFINITELY hear it! Unless>you sample faster than 108kHz, this 54kHz noise would show up as low>frequency aliasing.

Possible, but very very very unlikely. Most AD converters are oversamplingones nowadays. The filtering is done by a digital FIR filter. The samplerate is easily 64 fs or in some cases, 256 fs. This Nyquist frequency isway above 54 kHz, (sample rate is about 3 MHz - 11 MHz). As for the digitalfilter, 12 order eliptical is not uncommon.

Even if the filtering is done by analogue style filters, we are easilytalking 8-10 order filters and 54 kHz is more than an octave above 22.05kHz, so the attenuation of the aliasing is in the order of -48 to -60 dB.And then again, the aliased frequency of 54 kHz is around 10 kHz. Very hardto hear I have to say.

>2. If this signal went through any transistor, diode, or any other>exponential device (or even square law device), it could have easily>been modulated down to audible frequencies. This is the most likely>cause of the audible noise.

This I also don't think so. Any form of nonlinear modulation will result inharmonics of higher order, not lower. Of course, I could be mistaken ...now where did my textbook go? (I studied this in 3 rd year - about a yearago).

>I simply don't think it's reasonable to assume that the 54kHz noise on>its own added some mysterious unquantifiable "air" to the sound that>cannot be otherwise established in laboratory tests on human hearing.

It is reasonable. In the early days of digital audio I could easily pickout the difference between analogue and digital sound. 10 seconds oflistening to any source blindfolded, and I could tell you if it had beendigitised. I have a LP player (record player - vinyl). I still love thesound of vinyl - it is very very different and has a certain characteristicthat digital doesn't have. I have tried DATing the vinyl and it soundsdifferent after.

I haven't pulled out a broadband spectrum analyser so I cannot tell you howfar the frequency spectrum of vinyl is (I would reckon around 30-40 kHz,but I can't be sure). But it does sound different, and very different afterpassing through a DAT.

This is not to say that digital sound is bad. It is maturing now, and forconsumer grade products, getting very very pretty darn good I have to say.Probably in 5 years time, it would be indistinguishible from analog sound.It is still different, but the differences are getting very small.

5 years ago, I could tell them apart in 10 seconds. Now it takes me about3-5 minutes and I get the answer wrong about 25% of the time. That is howgood digital is getting.